High beam (main beam,full beam,driving beam) casts most of its light straight ahead, maximizing seeing distance, but producing too much glare for safe use when other vehicles are present on the road.

Low beam (dipped beam) has stricter control of upward light, and directs most of its light downward and either rightward (in right-traffic countries) or leftward (in left-traffic countries), to provide safe forward visibility without excessive glare or backdazzle.